Codon 12 Ki-ras mutation in non-small-cell lung cancer: comparative evaluation in tumoural and non-tumoural lung

Abstract

Summary Ki-ras activation by point mutation on codon 12 has been reported in non-small-cell lung carcinomas and in various models of experimental lung tumours induced by chemical carcinogens. The cellular targets for carcinogenic compounds of tobacco smoke are usually considered to be the cells of the bronchial mucosa or alveolar epithelium. However, little is known about preneoplastic events in bronchopulmonary carcinogenesis. The hypothesis of the presence of widespread target cells containing Ki-ras mutation was investigated by evaluating concurrent neoplastic and non-neoplastic bronchial and alveolar samples from 51 patients with non-small-cell lung carcinomas. The polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method used can detect one cell with a mutation on codon 12 among 102 normal cells. In tumour samples, a mutation was detected in 20% of adenocarcinomas, but in none of the adenosquamous or squamous cell carcinomas. No mutation was detected in the non-neoplastic bronchial or parenchymal samples. When using an enriched PCR-RFLP method detecting one mutated allele among 103 normal alleles a mutation was detected in 23% of adenocarcinomas. In conclusion, Ki-ras activation by mutation on codon 12 was not observed in non-neoplastic bronchial or parenchymal tissues in patients with bronchopulmonary cancers and does not appear to be a genetic event present in non-malignant epithelial target cells exposed to tobacco smoke.

Detection of codon 12 K- ras mutations in non-neoplastic mucosa from bronchial carina in patients with lung adenocarcinomas

“…In the present series of 19 lung adenocarcinomas, activated protooncogene K-ras by mutation on codon 12 was observed in eight lung adenocarcinomas (42%), as already reported previously (Rodenhuis et al, 1988;Slebos et al, 1990;Urban et al, 1996). However, similar results have been recently reported; for example Ronai et al (1996) detected K-ras mutation in 48% of a series of non-small-cell lung carcinomas.…”

“…The sensitivity of the assay was therefore controlled by a series of titration experiments. The limit of detection was 1 cell with homozygous mutation within a minimum of 10 3 cells with a wild-type K-ras gene, as previously reported (Urban et al, 1996).…”

“…This method is highly specific, as loss of the restriction site at the target is diagnostic for the presence of a mutation (Jiang et al, 1991;Urban et al, 1996;Behn et al, 1998). The enriched PCR/RFLP procedure is able to detect one mutated allele among 10 3 normal alleles, while a one-step PCR/RFLP analysis is only able to detect a K-ras mutation present in 1% of cells studied (Urban et al, 1996). Used as a control of this method, specific oligonucleotide hybridization gave similar results in previously published experiments (Urban et al, 1996).…”

“…K-ras codon 12 sequences were amplified (Perkin-Elmer Cetus thermal cycler) by an enriched polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) method, as previously reported (Kahn et al, 1991;Urban et al, 1996).…”

“…In a previous study, testing the hypothesis of the presence of widespread target cells containing K-ras mutations in the respiratory tract, we did not find any mutation of codon 12 of the K-ras gene in non-neoplastic distal bronchial or parenchymal tissues in patients with lung adenocarcinoma (Urban et al, 1996). Similarly, in a recent report comparing neoplastic tissue and contralateral bronchial mucosa, the authors failed to detect K-ras mutations in non-neoplastic cells (Behn et al, 1998).…”